MegaSack DRAW - This year's winner is user - rgwb
We will be in touch
Our house was built in 2007, so it's pretty good with energy in general. I'm sure the builders built to minimum standards though and there is definitely a fair bit of cold air behind the curtains at night.
Are top notch A rated windows significantly better than the run of the mill stuff? I would expect them to be expensive.
(please don't say 'just turn your thermostat down' etc etc)
What are you starting with in regard to U-value and emissivity?
What are your objectives?
Are you looking at reducing heat loss in the winter or a reduction in all year energy consumption?
Last conversation with a glazier was quite clear with the idea that triple glazing was only worth the expense if you were after noise reduction.
Are you doing this to save money or help the environment?
If it's the latter you'll probably find any incremental saving from new windows will be dwarfed by extra emissions of replacing 5 year old windows with newly manufactured ones.
What are you starting with in regard to U-value and emissivity?
No idea other than the fact it's a Wimpey home and they are stock 🙂
Are you doing this to save money or help the environment?
I'm not replacing windows any time soon, this post is to establish whether or not it should go on the end of the list of stuff to do after a load of other things.
Why yes, I am bored at work, how can you tell?
I'm not replacing windows any time soon, this post is to establish whether or not it should go on the end of the list of stuff to do after a load of other things.
I can think of more effective methods of improving year round window performance, and possibly for less money.
In a similar vein but as a (slight) hijack if you had what looked like a cheap floor to ceiling (say 2.5m x 2m) upvc window installed at least 5 years ago would a brand new up to date A rated window significantly reduce heat loss via this window in winter (Can currently feel the temperature gradient towards this window).
I can think of more effective methods of improving year round window performance
So can I. I'm just curious about windows, that's all.
I'm interested too, could one make inprovements by replacing the sealed units without redecorating problems?
Take a look at
Page 21, Max U value of 3.3 for windows in a 2007 new build (if I read it right).
Are top notch A rated windows significantly better than the run of the mill stuff? I would expect them to be expensive.
Unfortunately you're going to have to give a few more details than this. Current rating, the bigger the step, the greater the saving.
Orientation of the house, how many south facing windows and what sizes?
Without more details it'll be impossible to give a definitive answer.
Again what is your objective?
An A rated window will help reduce heat loss, but I couldn't possibly tell you how much without more details.
Will they reduce your energy consumption? I doubt it.
Same applies to nixie, reduce heatloss, yes. Reduce energy bill over the year, possibly not.
Objetive would be to reduce energy consumption. And I don't know the current rating. House has no windows facing south, only two of the bedrooms face west and get warm. Living room gets little sun.
Why would reducing heat loss not result in reduced energy consumption?
Have a read of this.
[url= http://gaia.lbl.gov/btech/papers/51913.pdf ]http://gaia.lbl.gov/btech/papers/51913.pdf[/url]
We've been able to get U-values of double glazed units' U-values down from 1,8W/m²K to 0,81W/m²K representing a 55% reduction in heatloss. The financial gains depend on lots of variables, back to power source, orientation and window size again.
Does reducing heat loss also reduce insolation then?
Why would reducing heat loss not result in reduced energy consumption?
Solar heat gain.
Wonderful in the winter to top up the heating and reduce consumption and the Low-e glass prevents heat loss. But in the summer, the same solar heat might just contribute to overheating of the property, it's the solution to this overheating that's likely to lose you any benefits you received in the winter. Air conditioning is expensive to run.
Geography will also determine how best to use the Low-e coating.
Have a flick through this.
[url= http://www.buildinggreen.com/live/index.cfm/2012/3/27/Window-Performance--the-Magic-of-Lowe-Coatings ]http://www.buildinggreen.com/live/index.cfm/2012/3/27/Window-Performance--the-Magic-of-Lowe-Coatings[/url]
Air conditioning is expensive to run
Remember I live in the UK and don't have air conditioning...
Does reducing heat loss also reduce insolation then?
Improving insulation is going to reduce heatloss in both the summer and the winter leading to overheating in the summer. You wouldn't wear your hat, gloves and thermals on a summer's day, would you?
The predictions are that we're going to witness more summers like the summer of 2003, which means that heat gain in the summer is going to become a much more serious problem, maybe not now, but if you're replacing windows that have a life expectancy of 20 years, it might be worth thinking about.
The glass itself is least likely to be the problem - the frames they sit in and how they were installed are more likely. There are far more variables in the frame and it's fitting than the units. Check around them to see how well they are sealed - especially outside underneath the sill. Also, do they have trickle vents in the frame? These often don't seal very well. However, you do need some air movement (unless you have other ventilation) to ensure enough air changes to prevent humidity and a build up of CO / CO2 in the room / house. You might have something in the wall that is bridging from outside to inside - poor design and building can cause this, especially around windows and doors.
Check around them to see how well they are sealed - especially outside underneath the sill.
In my case they are sealed badly, there are gaps in the sealant between frame and brick and a huge void behind it. Job for the summer is to remove all sealant, fill gap with (expanding) insulation, and reseal. Also thinking air gap blinds for the front window with a heavy curtain.
Improving insulation is going to reduce heatloss in both the summer and the winter leading to overheating in the summer
The amount of heat lost through the glass in summer is dwarfed by the fact that they are open though! Ok so it still gets warm, but I've got a long way to go before I get aircon.
Re curtains - you can get thermal backing for curtains, it's ace stuff.
The amount of heat lost through the glass in summer is dwarfed by the fact that they are open though! Ok so it still gets warm,
And don't the burglars just love that.
Re curtains - you can get thermal backing for curtains, it's ace stuff.
And what exactly do they do? I've seen some blinds that claim to reflect back 78% of the heat back into the room. I'm still waiting after two weeks for something to support that claim. I'm sure they do something, but what and how much? And how much are they? And will they keep your home secure?
I got a sample of those blinds through don simon - frankly ill be surprised if it does anything ......
I got a sample of those blinds through don simon - frankly ill be surprised if it does anything ......
Do you have a price for them (per m² if possible)?
I'm quite sure they'll do something, and I'm quite sure that 78% is a valid figure. What I'm not sure about, and what they won't reply to, is what this represents in the real world.
Gotta love numbers. (87% of the people agree with that statement). 😀
Can a window be 'energy efficient'?
You can't really increase a windows efficiency in it's use of energy.
Other than that I have nothing to add, although the above doesn't add anything anyway...so I have nothing constructive to offer the wider STW team.
although the above doesn't add anything anyway..
I'll pass this on to some of the experts linked to. 😆
So on the blog that ds linked to, there's a comment about a thin film applied on the inside of an existing window to lower heat loss. Is this likely to be the way to go in the future? It might be worth waiting to see.
Is this likely to be the way to go in the future?
If you're talking about Low-e, I think that's pretty standard on most new double glazing, but it only resolves one part of a more complex problem.
Of course, it all depends on your needs, you current situation, your pocket and your objective... The Future Advanced Windows article puts the dynamic window as a clearly superior window for performance, but we have to consider other limiting factors. And that's the fun bit. 😀
And what exactly do they do?
They insulate. You know, like jumpers and stuff. It's cheap, since it's only fabric, and no it doesn't protect from burglars since it's only curtains....
I am sensing scepticism.. I think you think I am asking for more than I actually am.
I am sensing scepticism..
Sceptisism of what?
They insulate like jumpers? I've already said thet the suppliers can't answer my question on effectiveness. Do they work against radiated heat, convection or conducted heatloss? How much heat loss? And at what cost?
You asked about energy efficient windows, I've told you about energy efficient windows. You have needs and will buy whichever product satisfies those needs. I can only point out the strengths and/or weaknesses of products and provide you with independantly sourced information. I can't control what you do with that.
The onkly point of contention is whether temperature are going to rise in the future because of climate chance, I'll let the experts fight over that one.
I kind of get the feeling of someone who doesn't want to accept the fact that have been presented to them.
If you have any more questions just ask me. 😉
[url= http://www.finehomebuilding.com/how-to/articles/understanding-energy-efficient-windows.aspx ]Here's some more glass stuff to keep your interest up.[/url]
I kind of get the feeling of someone who doesn't want to accept the fact that have been presented to them
Did I miss the facts in the thread?
They insulate like jumpers? I've already said thet the suppliers can't answer my question on effectiveness
Thick fabric has been considered good insulation for thousands of years. I expect they work by separating the air masses and preventing heat transfer by mixing, a bit of conduction, and a bit of convection. Radiant heat not so much.
My curtains seem to work quite well, but they are not the magic reflecting heat kind you are talking about.
Apparently.
My curtains seem to work quite well, but they are not the magic reflecting heat kind you are talking about.
Of course they do, but I assume you're not happy with that, hence your question about energy efficient windows.
If I can help you broaden your mind and look at alternatives, I am happy to do so.
If you're not interested, that's fine too.
If someone claims to reflect 78% of the heat back into the room, I'm within my rights to be sceptical and ask questions. If they can't answer the questions, should I accept what they say as fact.
Would you like me to dig out some more comparative tests? I just don't have them to hand at the moment.
Of course they do, but I assume you're not happy with that,
Well they don't work so well in the daytime, no 🙂
If I can help you broaden your mind and look at alternatives, I am happy to do so.
I am keenly interested in all energy saving ideas. However the original thread was about windows - what might the difference be in heat loss between typical modern cheap windows and some expensive A rated ones.
Well they don't work so well in the daytime, no
Depends on what you want them to do. 😉
Agreed that the original thread was
However the original thread was about windows - what might the difference be in heat loss between typical modern cheap windows and some expensive A rated ones.
Like many things the solution to a simple question can become a little more complex, you know, like "What bike should I buy?" Unfortunately you can't offer a starting point, so the questionis impossible to answer, but in general there will be an improvement. HTH.
The original question was followed by
Why would reducing heat loss not result in reduced energy consumption?
And I offered an answer to your objective of reducing energy consumption.
Anything else? 😀
CONTAINS EDITS.
Well yes, but I was hoping the question would be interpreted as something more specific than 'what bike?'. I mean I didn't ask 'how can I save energy?' or 'how much money will I save?' I did specify heat loss, didn't I? Ok I didn't, but I did say reduce energy consumption, and it's safe to assume I don't have aircon.
Something like W/m2 for different windows would have been useful.
But you don't know what the current u-value is, which was asked in my first post.
When you get the info, have a look [url= http://www.energysavingtrust.org.uk/In-your-home/Roofs-floors-walls-and-windows/Windows ]here[/url] and [url= http://www.energysavingtrust.org.uk/In-your-home/Roofs-floors-walls-and-windows/Windows ]here[/url] then send the info [url= http://www.sapservice.co.uk/ ]here[/url] to get the proper calcs done. 😉
And from my point of view it's exactly the same as asking what bike. 😐
I thought someone experienced in fitting windows might have an idea of typical values.
Or maybe I thought I'd get some experiences and opinions.
Unfortunately there are too many variables for it to be a simple solution and I'd be suspicious of anyone who says otherwise.
BFRC
[url= http://www.bfrc.org/index.aspx ]BFRC[/url]
Some interesting stuff down the page a bit:
[url= http://www.pilkington.com/europe/uk+and+ireland/english/building+products/7288c98c-62d8-4075-a50a-3702453c7cb7.htm ]pilkington glass[/url]
IMHO you'd need a lot of glass that was very exposed to warrant going A rated over B rated. Unless the rest of your house is spectacularly well insulated and sealed and everything else is super efficient of course.
Some interesting stuff down the page a bit:
pilkington glass
That's an interesting read for the defence of glass from the glass manufacturers Pilkington. 😉
Anyone can quote centre point glazing U values - i.e the glass, but the the window needs to be modelled to find an overall. Too may variables and highly likely most fall outside the 2.0 - 2.2 U value requirement (Bet its changed again).
I'll give you an example. 48m x 8m of curtain wall (big window) - Centre point U value 1.1 - o/a 1.975.
You want to save energy - turn the heating off.
Solar heat gain can be combated with a solar control coating, so overall savings can be had.
With most modern solar control coatings they are 'dual function' and also provide/replace the low E coating (as this will reduce the heating effect in the summer, and reduce heat loss in the winter).
With a 16mm argon filled cavity, a typical u-value (through the centre of the glass unit) will be 1.1 (sometimes 1.0 depending on coating). Compare this the old Pilkinton K coatings that give 1.5.
Another thing to consider is the spacer bar material, as this will effect overall performance of the glazing unit/window.
As has been said, you can get a double glazed unit down to a 0.8/0.9 u-value with krypton filled cavities, but a triple glazed unit will get 0.8 with argon fill (walls and roofs are typically insulated to 0.15-0.28 u-value for comparisson)
Overall performance also depends on ratio of frame to glazing, as (in my area at least) the frame has a worse u-value than the centre of the glass, so the average u-value of the opening is worse than just the glass alone.
To summarise, if you want the best possible performing glass/window, a high performance soft coat solar control coating, krypton filled cavity, warm edge spacer unit that is triple glazed is the best.
BUT unless the rest of your home is to 'Passivhaus' standards, you'll not really notice the difference.
In a few years time, triple glazing will become the new standard. It already is the standard in Germany, and the next edition of the building regs is likely to impose average u-values that will be best/easiest achieved with triple glazing.
My god, is it bad that I even bore myself sometimes?! 🙂
slackman99
Any chance of a link to this coating, please?
With most modern solar control coatings they are 'dual function' and also provide/replace the low E coating (as this will reduce the heating effect in the summer, and reduce heat loss in the winter).
I'd be very interested in seeing this 'dual function' coating, and its cost.
To summarise, if you want the best possible performing glass/window, a high performance soft coat solar control coating, krypton filled cavity, warm edge spacer unit that is triple glazed is the best.
How much more does all that cost over 2G and what are the performance improvements? And even then I bet it can be improved upon though. 😉
The frames are quite cool to the touch, despite being UPVC.
Biggest issue in our house though probably is the front door. Always cool in the hallway despite a heavy door curtain. But then it is the bottom of three floors so to be expected I suppose.
Any chance of a link to this coating, please?
If I may...
[url] http://www.velfac.co.uk/Projects/Glazing#Sun [/url]
Cheers Haze, I still can't see anything that is 'dual function'. The blurb says it's designed to reduce solar gain and glare, something it will do in the winter and the summer. The problem with solar gain is we want it in the winter but not the summer, this is the same for Low-e, it can only do one job. I'll go out on a limb and say it's a physical impossibility to reflect long wave infra red during the summer when it's not required then suddenly allow it to enter in the winter.
The second problem with permanent fittings is that there has to be a loss somewhere, the cheaper coating would appear to reduce VT, the more expensive, er, the cost? I can't see prices.
Back to the original point, I can't see a single fixed glazing product that doesn't change its characteristics as being beneficial all year round, it defies logic and probably physics. This means, to me, that windows as we know them are not the best solution when looking at reducing the energy consumption but part of a solution that can be improved upon.
This is why I said that Molly's question was too simplistic for the available solutions, and there's a lot of confusing/unclear information out there.
Loads of different glass out there. Solar control (limits heat into the building) / Low E (Reduces heat loss from the building).
A good Low E soft coat on a typical 16mm 90% Argon filled will give a 1.2 - 1.3 centre point U value - generally .1 less with a Swiss style spacer system, and provides a SC of around 0.6
A solar control glass coating will achieve a similar, maybe higher U value but have a SC of between 0.17 to 0.6. (Not really a requirement on a domestic buildings)
I've leave it down to the specialists but I do have a liking for Pilkington Suncool 50/25 on commercial projects requiring a high degree of solar control.
Energy efficiency and solar protection are different properties, one would surely compromise the other.
Windows should only be considered as part of an overall strategy, I'd probably only concern myself with top performing windows if the rest of my building was super efficient.
You asked about energy efficient windows, I've told you about energy efficient windows.
When Molgrips has a question he doesn't want an answer. He just wants to tell the world he has a question. 🙂
Lol 🙂
Energy efficiency and solar protection are different properties, one would surely compromise the other.
Probably, but both are required (or disirable) properties, aren't they?
Windows should only be considered as part of an overall strategy, I'd probably only concern myself with top performing windows if the rest of my building was super efficient.
Isn't this simply because of the costs involved? If there was a cheap solution available, wouldn't it make sense to start thinking a little differently?
Desirable yes, I have seen both specs used on the same facades though never in the same unit (albeit in my limited experience).
Isn't this simply because of the costs involved? If there was a cheap solution available, wouldn't it make sense to start thinking a little differently?
Was a subjective comment but yes, I wouldn't go spunking a fortune on windows if my building was thermally flawed.
But if they were cheaper then of course I'd consider it 🙂
the frames are the weak link.
upvc frames are hollow plastic. they are not air tight like the glass units and condense internally. wood is a far better frame material but high maintainance. i reckon the ideal would be tripple glazed units housed in wooden frames. but get ready for the bill!
makes me laugh when i pull perfectly good wood windows out to replace with upvc. i think its crap.
But if they were cheaper then of course I'd consider it
Now you've gone all vague on me again. 😆
Cheaper than what? Cheaper than 3G with all the bells and whistles, I'm quite sure that can be done and greater savings potentially.
Good curtains do a fantastic job of keeping the cold out.
Even better make you own 'shutter' from some sort of Kingspan type insulation that fits into the reveals snugly. There is a full on eco-mentalist round the corner who has a similar set up but of course uses sheeps wool that naturally fell off the sheep etc.
Cheaper than what?
Cheaper than they currently are.
I'm not from a commercial background and don't know the specifics, although I am aware that thermally broken composites (for example) are pretty expensive!
Cheaper than they currently are.
You've got me there! 😀
If we follow traditional paths then any improvements in performance are going to push the price up. I recently saw some 3G glass at £360 per m², beautiful as it was.... 😯
There was another example, or it might have been the same one, where the huge glass frontage retro-fitted some shading to combat solar gains.
If we're looking at prices like that, and depending on performance, then I'm confident in saying yes, there is a cheaper alternative.
I'd even say there's room to lower the glazing spec and then add shutters to work to the strengths of both systems and add extra benefits too.
The future is dynamic. 😉
I'd even say there's room to lower the glazing spec and then add shutters to work to the strengths of both systems and add extra benefits too.
Unfortunately shutters appear to be ugly (exposed roller) and expensive, of not ugly and even more expensive (hidden roller). I'd love to have them fitting on at least all the downstairs windows but cost is prohibitive. We lived in Germany when I was (much) younger and I used to love closing the shutters.
Brise soleil can look pretty good on larger facades, although I'm not sure how this might translate to smaller residential buildings.
Normal french-style shutters aren't ugly, are they? People might think you are pretentious though.
the frames are the weak link.
I did wonder about this. I am tempted to squirt some expanding foam in them.
Unfortunately shutters appear to be ugly (exposed roller) and expensive, of not ugly and even more expensive (hidden roller). I'd love to have them fitting on at least all the downstairs windows but cost is prohibitive. We lived in Germany when I was (much) younger and I used to love closing the shutters.
I agree with the ugliness aspect with an external box and guides, but things have moved on a bit. A hidden roller box doesn't have to be any more expensive, I'd reckon that if you're considering upgrading your 2G, you could fit shutter instead for significantly less than the 2G would cost you and I'd suggest with greater benefits and gains. But retro fitting is a bit more complicated and could be considered when upgrading your 2G.
Costwise they're not as expensive as you think, if you know where to go. 😉
Brise soleil is, of course, an alternative as are other shading solutions and would probably work in the UK as the sun is high in the summer and low in the winter, but they don't really prevent heatloss, do they?
A question of preferences, innit?
People might think you are pretentious though.
Let 'em think that as your pocketing the saved cash. 😉
I've been thinking about a new porch on the front as the current one is just an alloy box. Guess this could be made wider to cover the window too so the box was hidden. Hmmm
Any tips in where would be best to go for better prices?
Hi Don,
A couple of links below to the major glass/coating manufacturers (just as examples)
Saint Gobain: [url= http://uk.saint-gobain-glass.com/upload/files/skn144_brochure_internet.pdf ]Coolite SKN 174[/url]
Guardian: [url= http://www.sunguardglass.co.uk/SunguardProducts/ProductsbySeries/SeriesSelector/Results/index.htm?id=11002011&coatingid=5350 ]Sunguard[/url]
Pilks Suncool already discussed up the page
All the major glass manufacturers offer various solar control coatings that also perform the same function as the low E coatings these days, but as with anything, they cost more than a bog standard low E coating. Probably overkill for most domestic house though.
Thanks for that slackman99, it's all very interesting and I'll have to toddle off to look for some prices. A brief read still doesn't convince me that these products are
[url= http://singletrackworld.com/forum/topic/talk-to-me-about-energy-efficient-windows/page/2#post-3750854 ]
[/url]is the best.
That's not having a pop btw.
For me it's a question of understanding a bit more, but the Saint-Gobain features [i]
[/i] which is perfect for the summer but less good in the winter."SGG COOL-LITE SKN 144 II can be
used to improve the energy efficiency
of buildings by considerably reducing
overheating and the need for costly
air conditioning."
And I guess that two of the things that jump out at me about the Guardian glass is a VT of 52% and W/m²K of 1,3.
My point being that while glass is good and there is plenty of technology and muchas advances etc, it shouldn't be considered the best and can be used with other products the complement each other.
As much as I believe what I'm doing is not a suitable solution for everyone, but it is a valid solution for many and should be considered.
nixie, you could do worse than dropping me an email.
Guardian u-value of 1.3 is with an air filled cavity. 1.0 with argon filled. Argon filled is standard in commercial glazing.
1.0 is as low as currently available with an argon filled double glazed unit (as far as i'm aware).
A 6T-16-6T SGG Coolite SKN174II will set you back in the region of £70/sqm plus energy surcharge.
Like for like, Guardian products are cheaper than Saint Gobain and Pilks. Glaverbel/AGC slightly cheaper again.
And which ones do you sell? 😉
I don't sell any. I buy. Used to work for a company owned by Saint Gobain, and still bought Guardian glass as the rates were/are better (for commercial projects)for an equivalent product.
That will explain why you see them as being the best solution. 😉
1.0 is as low as currently available with an argon filled double glazed unit (as far as i'm aware).
Can I make you aware of a double glazed test I've had done taking the value down to 0,81W/m²K, bog standard double glazing of 1,80W/m²K to start with. 😀
I've read through all of this thread in a weird kind of masochistic way.
My contribution; molgrips, get some super thick curtains.
Crikey's right, curtains will work.
[url= http://gentledescent.wordpress.com/2009/03/22/insulating-effect-of-curtains/ ]http://gentledescent.wordpress.com/2009/03/22/insulating-effect-of-curtains/[/url]
Thank you don simon. I always tell the wife and kids that there is little point having the heating on in the winter and having the curtains open. We do have big double glazed bay windows, but it is noticeably warmer when the curtains are closed.
In the summer, when I am on nights, keeping the curtains closed also helps to reduce the heat build up in the room until the late afternoon. I have a southwest facing house which gets roasted in the summer and wind chilled in the winter.
I cannot believe that my life has come to the point where I cannot find anything better to do than discuss curtains, windows and the heat/cold related efficiency thereof...
keeping the curtains closed also helps to reduce the heat build up in the room until the late afternoon.
You should really put them on the outside to maximise the benefit, if you want to go into the minute details, best left for when you have insomnia.
Might make them
a) difficult to draw,
b) a wee bit dirty,
c) add to the neighbours consternation... 😉
Can't have everything, eh? 😆
Don,
How have you taken a 1.8 centre pane dgu and turned it in to a 0.8 centre pane dgu?
An no, windows aren't the most energy efficient way to create an external part to your home. A highly insulated wall would keep more heat in in the winter, more heat out in the summer, but would be a little dark.
There aren't many buildings that don't have some form of glazing in them, so i'd hardly say that I was trying to say windows/glazing are most energy efficient simply because i'm in the industry.
On a side note, draughts take a hell of a lot of heat out of houses. If you have trickle vents on the windows (the small vents above the glass) then these usually lose a lot of heat. Sealing these up can often help keep heat in
My contribution; molgrips, get some super thick curtains.
You can't ahve been reading that closely, I already have thick curtains 🙂
On a side note, draughts take a hell of a lot of heat out of houses. If you have trickle vents on the windows (the small vents above the glass) then these usually lose a lot of heat. Sealing these up can often help keep heat in
Sealing trickle vents can cause a build up of damp and is not recommended.
Blinds installed within the DGU's might be a way of improving the thermal performance of windows, pricey though.
[url= http://kalablinds.files.wordpress.com/2012/03/4-bed-dwelling-jdpwindow.pdf ]Window 1,8W/m²K[/url]
[url= http://kalablinds.files.wordpress.com/2012/03/4-bed-dwelling-jdpwindow-with-blinds.pdf ]Window + 0,81W/m²K[/url]
😉
pricey though.
Not as pricey as you think.
You can't ahve been reading that closely, I already have thick curtains
Now who's not reading closely? 😆
*applauds don simons work and views*
Until you know the (woeful likely) U and psi values and airtightness of existing house (as built, not calculated) it is like whacking an XTR rear mech on a (likely) Halfords £99 special.
That appears to show that you've taken a 1.8 u value window, put it in a cavity with a blind and come up with a lower u-value. The read out doesn't really mean much to me as it doesn't show any of the properties of the window. It appears to be comparing a window unit with a window built into a highly insulated wall?
Interstitial blinds (blinds in the unit) don't improve thermal performance of the unit other than cutting out light (as would a normal much cheaper blind). They do however look swish.
I seem to have veered massively for the OP's original question though.
To sum up, unless you have an ultra well insulated and draught proofed home, changing from a B rated window to an A is unlikely to make any significant/noticeable difference.
Are new bulid houses that bad? We pay £30/mo in gas in the winter, I thought that was ok.
Ok so ideally i'd like to pay far less... I am always thinking about creative solutions to heating the home.
Anyone put solar hot water on a wall rather than a ceiling?